1. Field of the Invention
This invention relates to a resist material, and a pattern forming process using the resist material. 2. Description of the Related Art
As the integration density of semiconductor devices has become higher and higher in recent years, a resist material capable of forming a miniature pattern has been required.
In patterning processes, a technology called "two-layered resist process" has been employed which comprises the steps of forming a lower resist layer for levelling on a to-be-patterned material (to-be-etched material), then forming an upper resist layer, exposing this upper resist layer, developing, and transferring the resulting pattern to the lower resist layer to obtain a mask pattern. In this case, a resist material for constituting the upper resist layer must have performance capable of withstanding at least etching for transferring the pattern to the lower resist layer (generally O.sub.2 RIE, that is, reactive ion etching using oxygen).
Polyacrylate type resists, polysiloxane type resists and polysilane type resists, have high etching resistance due to the introduction of silicon (Si) into an ester portion of the resist materials. They are known as the materials for the upper layer resist material in the multi-layer resist process described above (for example, Japanese Unexamined Patent Publication (Kokai) Nos. 2-191957, 2-239251, 3-217845, 3-261952 and 4-42229). In all of them, development is based on the difference of molecular weights between exposed area at the time and unexposed area. As a result, sharp patterning cannot be conducted and swell of the resist pattern occurs at the time of development, limiting their usefulness for obtaining miniature patterns. Because of the ever-increasing integration density of semiconductor devices, this is a significant drawback.